a) Field of the Invention
The invention is directed to an immersion microscope objective. Objectives of this kind are used, for example, in laser scanning microscopy (LSM), to observe the three-dimensional structure of biological objects, particularly tissue cultures and cell cultures. The cells are in a vessel with a solution. The vessel is closed by a thin coverslip. The side of the microscope objective facing the object is located on the other side of the vessel in an immersion liquid—at least the lens surface defining the objective on this side must be in the solution. In this connection, it is required that the refractive indices of the liquids on both sides of the coverslip are similar because only then can the layers of the specimen be imaged sharply at different depths. Since the living biological objects are generally in an aqueous solution, primarily water or glycerin are used as immersion liquids. Further, in order to be able to resolve the fine structure of the objects, immersion microscope objectives of the kind mentioned above need a high numerical aperture.
b) Description of the Related Art
Various immersion microscope objectives are known from the prior art. For example, U.S. Pat. No. 5,530,590 provides a microscope objective with three different variants, each with a numerical aperture of 1.15. This objective comprises three groups of lenses, the second lens group being displaceable relative to the two other groups along the optical axis in order to adapt the objective to the thickness of the coverslip for closing the sample, i.e., to compensate the spherical and chromatic aberrations which occur in objectives of this type having a high numerical aperture and which vary with this thickness.